According to the virtualenv docs only POSIX systems follow the
structure "/path/to/venv/bin/", while windows systems use
"/path/to/venv/Scripts" for the location of the binary files, most
importantly including the python interpreter (see:
https://virtualenv.pypa.io/en/stable/userguide/#windows-notes).
* lisp/progmodes/python.el (python-shell-calculate-exec-path): Use the
"/path/to/venv/Scripts" for `windows-nt' machines.